Efficacy of neem oil for control of stored cowpea seed beetle

Abstract

Cowpea beetle, Callosobruchus maculatus, is a major pest of stored cowpea. Farmers use mostly synthetic insecticides to control the pest in store, although biopesticides such as neem oil have been proven to be a sustainable alternative. The objective of this study was to determine the effective and feasible rates to enhance cost-effectiveness of neem oil in the management of C. maculatus in stored cowpea grains. A laboratory experiment was conducted, in which sterilised healthy cowpea grains (50 g each) were treated with neem oil at 0, 0.5, 0.75, 1 ml and 0.05 g ACTELLIC Gold Dust® (16 g kg^-1 Pirimiphos methyl + 3.6 g kg^-1 Thiamethoxam). The experiment was laid out in a completely randomised design, with four replications. Results revealed that adult female C. maculatus laid eggs on all the treated cowpea grains, except those treated with 1.0 ml of neem oil. However, no adult emergence and damaged grains were recorded from grains treated with 0.50, 0.75 and 1.0 ml of neem oil. This study has shown that cowpea grains treated with 0.50, 0.75 and 1.0 ml of neem oil outperformed those treated with insecticide actellic dust. Among the rates of neem oil assessed, there was no significant difference between their effect on the management of C. maculatus. Thus, 0.50 ml of neem oil per 50 g of cowpea grains is the most cost-effective rate for the management of C. maculatus in stored cowpea grains.